The present invention relates to an aircraft nacelle comprising a deformable connection between an air intake and a power plant.
An aircraft propulsion assembly comprises a nacelle in which a power plant connected to the rest of the aircraft by means of a pylon is arranged, in a substantially concentric manner.
As shown in FIG. 1, the nacelle comprises, at the front, an air intake 10 by means of which an air flow can be channeled towards the power plant 12, wherein a first portion of the inflowing air, termed the primary flow, passes through the power plant in order to participate in combustion, and the second portion of the air flow, termed the secondary flow, is driven by a fan and flows in an annular duct delimited by the inner wall of the nacelle and the outer wall of the power plant.
For the remainder of the description, the longitudinal direction corresponds to the direction of the axis of rotation of the fan of the power plant.
The air intake 10 comprises a lip 14; that surface of the lip which is in contact with the aerodynamic flows extends, inside the nacelle, in the form of an inner duct 16 of substantially circular section and, outside the nacelle, in the form of an outer wall 18 of substantially circular section. The power plant comprises a duct 20 which may be arranged in the continuation of the inner duct 16.
As shown in FIG. 2, the air intake 10 is connected to the power plant 12 by a connection which comprises, at the level of the power plant, a first annular flange 22 secured to a second annular flange 24 of a panel which delimits the duct 16 or of an interposed part 26, termed bracket, connected to the panel which delimits the duct 16. The two flanges 22 and 24 are clamped against one another, at the level of a junction plane 28 which is substantially perpendicular to the longitudinal direction, and are held in that position by connecting elements 30, for example bolts or rivets, which pass through the flanges 22, 24 and extend parallel to the longitudinal direction.
In terms of structure, the air intake 10 comprises a first frame, termed the forward frame 32, which connects the inner duct 16 and the outer wall 18 delimiting, with the lip 14, an annular duct 34, and a second frame, termed the rear frame 36, which connects the inner duct 16 and the outer wall 18 close to the junction plane 28.
The rear frame, for its part, makes it possible to take up bending, rotational or other forces which act on the air intake such as, for example, the weight of the air intake and the forces induced by the aerodynamic flows.
According to one embodiment, the rear frame 36 is connected to the duct 16 either directly or via an interposed part or bracket 38 (shown in detail in FIG. 2) one leg of which is connected to the duct 16, the other leg being connected to the rear frame 36.
The rear frame 36 is connected to the outer wall 18 either directly or via a bracket 40 (shown in FIG. 1) having a T-shaped cross section, wherein the rear frame 36 is connected at the level of the foot of the T-shaped bracket, and wherein the head of the T presses against the inner face of the outer wall 18.
In the event of fan blades failing, the duct 20 of the power plant tends to undergo substantial deformation since it is designed to absorb, by deformation, the energy of the broken blades. At the level of the air intake, the inner duct 16 is made of a composite material and its mechanical properties are more limited than those of the duct 20 of the power plant, in particular in terms of bending strength.
In addition, in order to limit the risks of the panel or panels, which form the inner duct 16 of the air intake, coming loose, it is expedient to limit the spread of the deformations from the duct 20 of the power plant towards the inner duct 16 of the air intake.
To that end, a first solution consists in stiffening the rear frame and/or the connection between the air intake and the power plant so as to limit the spread of the deformations towards the inner duct 16 of the air intake.
Another solution consists in designing a rear frame and/or a connection between the air intake and the power plant which may deform so as to limit the spread of the deformations towards the inner duct 16 of the air intake.